Field of the Invention
The invention relates generally to Vertical Take-Off and Landing (VTOL) fixed wing aircraft.
Description of Related Art
Since the early days of aviation, designers and engineers in both the commercial and military aerospace fields have envisioned fixed wing aircraft capable of taking-off from a runway no larger than its own shadow, and then transitioning to high speed forward flight. However, the reality of vertical take-off and landing (VTOL) flight for high performance commercial aircraft and military fighters has proven to be a perplexing and obsessive goal. Helicopters and autogyros, both types of VTOL non-fixed wing aircraft, are often deemed too fragile, too slow, and too vulnerable for safe air commerce and/or aerial combat.
The well-known “VTOL Wheel,” produced by AHS International of Fairfax, Va. and/or its Vertipedia database, lists some forty-five various aircraft types within the broad category of VTOL capable. Within these forty-five aircraft types, one might find some fifteen various thrust options and some four different propulsion methods. To-date there has been several successful high speed military VTOL aircraft. The MD AIBAE A V-8 Harrier and the Lockheed Martin F-35 incorporate rotating jet nozzles thrust vectoring and/or lift fan technology (F-35).
Notwithstanding past and present accomplishments in the VTOL field, there is a continuing need and desire to design, develop and demonstrate a VTOL fixed wing aircraft with exceptional performance in vertical and cruise flight and operational capability through transition from vertical to forward flight. Specifically, the VTOL fixed wing aircraft should be capable of sustained high-speed flight, e.g., between ˜300 kt and 400 kt. the VTOL fixed wing aircraft should be capable of hover efficiency within 25% of an ideal power loading (at standard sea level conditions) and cruise lift-to-drag ratio no less than 10. Preferably, the VTOL fixed wing aircraft should have a gross weight between 10,000 lb-12,000 lb, a useful load no less than 40% of the gross weight and a payload capacity of at least 12.5% of the gross weight.
Many such aircraft seeking to meet these design criteria utilize open-exposed rotors or propellers that rotate between VTOL and flight modes. However, there is an ever-present concern that open-exposed rotors or propellers within the human safety zone could be hazardous, and at the very least frightening. In hostile military environments, open-exposed rotors or propellers are also more vulnerable to flying metal shrapnel and small arms fire. Another downside to rotating engines or propellers is that rotation changes the thrust point. Rotating mechanisms, and the dedicated power supplies that are needed to provide the mechanical rotating transition, add significantly to center of gravity issues and make it very difficult to sustain controlled flight.
Ducted fans have also been proposed for perimeter rotating blades, however the intake (unscreened) is unfavorably referenced as a vacuum for increased foreign object debris (FOD) ingestion along with the increased drag from the circular duct detracting from horizontal flight. The applicant is not aware of any ducted fan aircraft that is able to sustain forward flight speeds greater than 270 kts.
Another downside exhibited by many current technology VTOL aircraft types relates to excessive noise. Rotor blade interaction is the result of large rotor blades interacting with retreating blades compressing airflow downward on the vertical axis cumulating a high decidable, mid-range acoustic signature that can often be heard for miles ahead of the aircraft. Furthermore, adverse Yaw tendencies are controllability issues around the Y and X axes that cause adverse gyroscopic forces from open, exposed rotor blades and propellers and engine rotation.
There is therefore a need for new and improved VTOL design solutions for fixed wing aircraft. The new and improved design solutions should retain a conventional seating arrangement and utilize a single point VTOL lift source that does not require powered cross shafting. Additionally, the new and improved design solutions should not require large exposed pivoting engines, propellers or ducted fans. Finally, the new and improved design solutions should eliminate any rotor blade interaction and adverse Yaw tendencies.